The present invention relates to an image forming apparatus of an electrophotographic system such as a copying machine, a printer and a facsimile telegraph, wherein a charging means, an imagewise exposure means and a developing means are arranged around an image forming body, and a toner image formed on an image carrier is transferred onto a transfer member (hereinafter referred to as a recording sheet) and fixed thereon.
For two-sided copying in the past, an image for one side formed on an image forming body is first transferred onto a recording sheet and fixed thereon, and the recording sheet is stored temporarily in reversing/sheet-feeding unit, and then is fed from the reversing/sheet-feeding unit in a synchronization with an image formed again on the image forming body so that the image for the other side is transferred onto the recording sheet and fixed thereon.
In the two-sided copying apparatus, a recording sheet is fed to a reversing/sheet-feeding unit and is passed through a fixing unit twice. Therefore, reliability of conveyance of the recording sheet has been low, resulting in a cause for jamming. In contrast to this, Japanese TOKKOSHO Nos. 49-37538 and 54-28740 and TOKKAIHEI Nos. 1-44457 and 4-214576 disclose a technology wherein toner images are formed on both sides of a recording sheet and then are fixed collectively on the recording sheet. In each of TOKKAIHEI Nos. 1-44457 and 4-214576, in particular, there is disclosed a method wherein a plurality of toner image receiving bodies each being composed of an image forming body, a charging means, an imagewise exposure means and a developing means are arranged in parallel on a toner image receiving body so that a two-sided copy of color images may be formed.
In the two-sided color image forming proposed by TOKKAIHEI Nos. 1-44457 and 4-214576, however, image deteriorations such as doubling, toner scattering and frictional damage tend to be caused because color toner images each being different in color are superimposed on an intermediate transfer body, although conveyance of a recording sheet is improved.
In contrast to this, the inventors of the present invention have studied a two-sided image forming apparatus wherein toner images formed on an image forming body are collectively transferred onto a belt-shaped intermediate transfer body (toner image receiving body) temporarily, then toner images are formed on the image forming body again, and the toner images on the toner image receiving body and the toner images formed again on the image forming body are transferred respectively onto both sides of a recording sheet (a transfer member). However, it is not easy to clear jamming of the recording sheet in the sheet feeding path between the image forming body and the belt-shaped toner image receiving body. For easy jam clearance, therefore, the inventors have studied the structure wherein an apparatus is divided into an upper shell and a lower shell with a sheet-feeding path between, in which, however, a transfer-separating means provided to face a toner image receiving body obstructs jam clearance at the edge on the part of a fixing means, causing a problem that the transfer-separating means is damaged, and, in particular, a discharging electrode provided on the transfer-separating means is damaged.
The inventors have also studied that a conveyance section with spurred wheels which is provided between a toner image receiving body and a fixing means so that a recording sheet having on its both sides toner images formed may by conveyed without suffering damage of the toner images from the toner image receiving body to the fixing means. However, there still is a problem in that the spurred wheels may be damaged in the course of jam clearance or in that the spurred wheels can hurt human hands.